1. Field of the Invention
The present invention is directed generally to optics. More particularly, the present invention relates to beam positioning and pointing for use in lithographic processing.
2. Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a substrate or part of a substrate. A lithographic apparatus may be used, for example, in the manufacture of flat panel displays, integrated circuits (ICs) and other devices involving fine structures. In a conventional apparatus, light is directed to a patterning device, which may be referred to as a mask, a reticle, an array of individually programmable or controllable elements (maskless), or the like. The patterning device may be used to generate a circuit pattern corresponding to an individual layer of an IC, flat panel display, or other device. This pattern may be transferred onto all or part of the substrate (e.g., a glass plate, a wafer, etc.), by imaging onto a layer of radiation-sensitive material (e.g., resist) provided on the substrate. The imaging may include the processing of light through a projection system, which may include optical components such as mirrors, lenses, beam splitters, and the like. Other components or devices may exist in a lithographic apparatus that can also contain optical components.
The positioning and pointing of a light beam used in lithography is conventionally accomplished using closed-loop beam steering. In closed-loop beam steering, one or more mirrors (typically at least two) can be controllable in X and Y rotations (Rx and Ry). The mirrors may be adjusted based on feedback from one or more beam position sensors and/or tilt measurement sensors. Although some systems use a single lens to control pointing (i.e., telecentricity) of the beam, in which the single lens is shifted in-plane (i.e., controllable in X and Y) to change beam pointing, conventional systems do not include both beam positioning and pointing without adding mirrors. The addition of mirrors requires additional volume for folding and may also produce undesirable polarization effects for large angles of incidence. The need to add mirrors also increases system cost.